Accumulated Other Comprehensive Loss - Reclassifications (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	$ (17,088)	$ (17,049)	$ (55,873)	$ (46,898)
Total net of tax	39,649	42,842	135,809	118,056
Interest and dividends on investment securities (taxable)	67	87	283	576
Interest expense	(46,796)	(37,057)	(125,570)	(112,074)
Total reclassifications, net of tax	(1,147)	(2,093)	(3,970)	(5,573)
Unrealized gains (losses) on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	4		4
Non-credit impairment losses on AFS securities before tax:
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	40		166
Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Total reclassifications, net of tax	(1,132)		(3,963)
Defined benefit pension plan:
Reclassification Out Of Accumulated Other Comprehensive Loss
Amortization of net loss	(101)	(71)	(303)	(215)
Tax effect	42	29	126	87
Total reclassifications, net of tax	(59)	(42)	(177)	(128)
Reclassification Out of Accumulated Other Comprehensive Income (Loss)
Reclassification Out Of Accumulated Other Comprehensive Loss
Interest expense	(1,930)	(3,578)	(6,762)	(10,146)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Unrealized gains (losses) on AFS securities before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Gains (losses) on securities transactions, net	6	(10)	5	258
Tax effect	(2)	4	(1)	(96)
Total net of tax	4	(6)	4	162
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Non-credit impairment losses on AFS securities before tax:
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	(27)	(37)	(117)	(240)
Total net of tax	40	50	166	336
Interest and dividends on investment securities (taxable)	67	87	283	576
Reclassification Out of Accumulated Other Comprehensive Income (Loss) | Unrealized losses on derivatives (cash flow hedges) before tax
Reclassification Out Of Accumulated Other Comprehensive Loss
Tax effect	798	1,483	2,799	4,203
Total net of tax	(1,132)	(2,095)	(3,963)	(5,943)
Interest expense	$ (1,930)	$ (3,578)	$ (6,762)	$ (10,146)